1. Field of the Invention
The present invention relates to a phosphor material and the forming method thereof, and more particularly to a phosphor material with carbon and nitrogen co-doping and an application of phosphor material to improve the luminous efficiency of the light emitting component.
2. Description of the Prior Art
Currently, for the light emitting diodes (LED) application, the white luminous device will gradually replace the traditional tungsten lamp and fluorescent lighting, because of the following characteristics (1) Small size and suitable for the illumination of array package and can apply for any combination of different colors; (2) Long usage life, the usage life can be up to 10,000 hours, and is longer than traditional incandescent light bulbs for more than 50 times; (3) Durable, the encapsulation of white luminous device is transparent resin which can use for the shock resistance and impact resistance; (4) Environmental, the luminous device did not contain mercury therein and no pollution and waste disposal problems; and (5) Energy saving and low power consumption, in general, luminous device is about ⅓ to ⅕ times the power consumption of incandescent light bulbs.
The so-called “white light” usually means a mixed light of multi-colors which is generated by the white light can be seen by the human eyes, and includes at least two or more kinds of color light wavelength. For example, the blue light is mixed with yellow light that can obtain the white light with two wavelengths, and blue light is mixed with green light and red light that can obtain the white light with three wavelengths.
The white light emitting diode can be divided into an organic light emitting diode and inorganic light emitting diode according to the material used in the manufacture. The illumination for the white light source includes three manners. First, the white light luminous module is composed by red, blue, and green light emitting diodes which include higher illumination efficiency and higher color rendering. However, because of the grain with different color have different grain epitaxial materials so as to produce different voltage characteristics. Therefore, the manufacturing cost is high so that the circuit design is complex and difficult to mix light.
Second, the current mainstream is white light emitting diode that is made by the blue light emitting diode to excite yellow YAG phosphor which is proposed by Nichia Corporation. Optical glue is mixed with yellow YAG phosphor is coated outer of blue light emitting diode chip, and the blue light emitting diode chip can emit the wavelength of blue light is range about 400 nm to 530 nm so as to excite yellow phosphor to generate yellow light and yellow light is emitted by remaining blue light cooperated with yellow light so as to generate the white light with two wavelengths that is mixed by blue light and yellow light.
However, such white LED has many limitations for illumination, the main reason as follows: because the blue light is the most part of the emission spectrum such that white LED has high color temperature and the color temperature is uneven. For above reasons, the effect between the blue light and yellow light need to improve so as to reduce the intensity of blue light or to increase the intensity of yellow light. Furthermore, because the wavelength of blue light-emitting diodes will vary with the temperature increase thus resulting in color control for a white light source is not easy. In addition, the color rendering of white LED is poor due to the lacks of red light.
The third is that ultraviolet light emitting diode excites the blue phosphor, green phosphor and red phosphor mixed with a certain proportion in the optical glue so as to obtain a white light with three wavelengths. Such white light LED can be combined after manufacturing the phosphor material of three primary colors separately and thus the process flexibility and nature are better than the previous two white LEDs.
Presently, the synthesis of the phosphor includes (1) Solid-state reaction method. This method disposes the reactant in the gas pressure sintering furnace to react and thus can be called gas pressure sintering method (GPS). The host lattice for white LED is composed by metal oxide, metal element and metal nitride and silicon-containing compound are reacted with nitridation reaction under rich-nitrogen and high temperature environment. The earliest and most commonly used silicon-containing compound is Si3N4, for the chemical inertness of silicon-containing compound, the solid-state reaction method is performed under an environment with high temperature (ranges from 1500° C. to 2000° C.) and high pressure nitrogen (ranges from 10 atm to 100 atm), and thus the reaction requires the expensive equipment and high cost. (2) Carbothermal reduction nitridation method (CRN). The different between CRN method and solid-state reaction method is that carbon as a reduction agent in the nitridation reaction so as to the reaction is performed under the lower pressure and rich-nitrogen environment (ranges from 1 to 5 atm). However, the duration of the reaction is longer about eight hours. In addition, the carbon content needs to control accurately because of excessive carbon will generate silicon carbide that will affect the fluorescence intensity. In the light of above problem, a carbon remove step is required to perform after nitridation reaction is completed, but the residual carbon within the product is not easy to completely remove, although such method can react in a lower nitrogen pressure, but the reaction will be caused time-consuming, energy-consuming and steps complicated problems. (3) Gas-reduction nitridation method (GRN). The theory is same as that of CRN method, but the different is that the organic gas such as methane substitutes the carbon as the reduction agent to perform nitridation reaction. Although this method resolves the excessive carbon problem, but this method utilizes gas and the reaction is carried out at high temperatures, such that the reaction has extremely dangerous and has time-consuming and energy-consuming problems. (4) Hydrothermal method. The reactant is usually nitric acid compound which dissolve in the solvent and the aqueous NaOH is added to adjust the pH value. The reaction is stirred at low temperature (about 200° C.) and then the precipitates are generated from the reactant. The precipitates (can be regarded as precursors) is performed with wash, centrifugation, filtration and drying and then sintering in a high temperature furnace with nitrogen environment and the hydrogen gas as the reduction gas is introduced into the high temperature furnace. The advantage of this method is that the reactant is evenly mixed by the step of dissolution and precipitation, and the sintering temperature is about 1000° C. to save energy effectively. The disadvantage is that the reaction step is more complicated and the reaction sometimes requires hydrogen to perform reduction, and thus this method has safety concerns. In addition, the crystalline phase for the synthesized product is weak and has lower fluorescent luminous efficiency so as to be improved. (5) Combustion synthesis. The reactants include metal, metal oxide and metal nitride and are mixed uniformly to dispose in the reactor. Then, the pressure of nitrogen is adjusted up to 2.0 to 8.0 MPa so as to ignite above reactants. The advantage of this method is a simple process step, less energy-consuming and simple equipment and thus it can be performed with mass-production and lower cost. However, the reaction must be carried out under extremely high pressure to improve the conversion rate so that the safety of synthetic requires being concerned and is not suitable for the industrial application. If the reaction pressure is lower, the product may result in improper control of agglomerating or can not be ignited, so as to the conversion rate is lower and the grinding step must be complicated. In addition, because the reaction is heating and cooling rapidly, so the product may contain a crystal defects with high concentration, such that the fluorescence intensity of the phosphor is poor.
According to conventional prior art, the nitridation reaction for preparing phosphor is performed at high temperature and under high pressure environment, as Si3N4 is used for the above described solid-state reaction method which must be performed at a high temperature (1500˜2000° C.) and under nitrogen pressure (10˜100 atm) environment, and the reaction requires expensive equipment and high cost. In addition, by using CRN method, the carbon is used as reduction agent that is added into the nitridation, but the excess carbon will affect the phosphor intensity. Furthermore, GRN method using organic gas such as methane as a reduction agent for the nitridation reaction, and the reaction is carried out by using a gas at high temperature, so the reaction will be dangerous and has time-consuming and energy-consumption problems. Moreover, in the past, for preparing the nitride phosphor or oxynitride phosphor, the nitride-containing compound is merely mixed and heated with the additional compound, and the mixture such as oxide is composed by the carbon or nitrogen is performed reduction reaction for nitridation but the characteristics of the phosphor can not be obtained sufficiently, and the nitrogen source such as alkali metal nitride or alkaline metal nitride has a poor operability problem.
Therefore, the nitrogen atoms in the nitrogen source can be used as the host lattice of nitride phosphor or oxynitride phosphor. On the other hand, the nitrogen source must be reacted sufficient to prevent incomplete reaction so as to cause lattice defects, and light illumination efficiency decrease. Moreover, according to conventional nitride or oxynitride manufacturing method, by using the liquid phase sintering of the firing process, the bonding between the particles is extremely hard, in order to obtain the target particle order of the phosphor, the crushed powder processing must be performed. In addition, when the crushed condition is more severe for phosphor, the chance of introduction of contamination is increased and the defect is introduced into the particle surface so as to affect the phosphor characteristic and the light emitting characteristics are deteriorated to affect the luminous efficiency. The synthesis of currently nitride phosphor or oxynitride phosphor is performed at high temperature and under high pressure, spent a longer reaction time or is performed with complicated steps, and thus the yield is not large and high production costs is required.
According to the aforementioned description, the synthesized phosphor is limited by manufacturing method, such that the reaction is performed at high temperature, under high pressure and complicated operation steps. According to the change of the crystal structure of phosphor, the change in the light emission characteristics is introduced, such as the illumination wavelength shift and the drop in the luminous efficiency. Thus, the prescription of raw material needs to be adjusted to obtain suitable raw recipe illumination wavelength and better luminous efficiency. Therefore, a preparation method must be developed for various phosphors, such as red phosphor, green phosphor and blue phosphor by simple process, low cost, the raw materials can obtain easy and excellent operability conditions and when the crystal lattice of phosphor is not changed, the luminous efficiency can be increased. Furthermore, the synthesized phosphor or commercially available phosphor also can use such preparation method for increase the illumination efficiency.